a=x3-2x2+x-4 b=2x3+5x-4 c=-4x2+x-1,
2a-(b+c)
=2(x3-2x2+x-4)-(2x3+5x-4-4x2+x-1)
=2x3-4x2+2x-8-2x3-5x+4+4x2-x+1
=-4x-3